Non-agglomerating mixed bed ion exchangers

ABSTRACT

The invention relates to a process for producing non-agglomerating mixed bed ion exchangers or mixed bed components.

The invention relates to a process for producing non-agglomerating mixedbed ion exchanges or mixed bed components.

BACKGROUND OF THE INVENTION

The use of mixed bed ion exchangers is prior art in the desalting ofaqueous solutions. Surface interactions between the cationic and anioniccomponents of the mixture lead to the formation of agglomerates(“clumping”) and thereby to poor flow behaviour. Furthermore, theperformance of such mixed beds is unsatisfactory. In addition theagglomeration prevents effective regeneration of the ion exchange resinsfor which the mixture must be fractionated as completely as possibleinto its components.

To prevent the unwanted clumping in mixed beds, diverse methods havebeen described such as, for example a) the treatment withwater-insoluble ion exchange particles in U.S. Pat. No. 4,347,328 wherehigh amounts used and high washwater volumes are required in order toremove excess ion exchange particles again or else b) the treatment withwater-soluble resinous polyelectrolytes according to U.S. Pat. No.2,961,417, U.S. Pat. No. 3,168,486, U.S. Pat. No. 5,902,833, U.S. Pat.No. 6,060,526 or EP-A 1 291 083. The water-soluble polyelectrolytes fortreating the anion exchange component are water-soluble resinouspolyelectrolytes such as polymeric acrylic or methacrylic acid(derivatives), but preferably sulphonated polyvinylaromatics, and veryparticularly preferably polystyrenesulphonic acid (PSS). Depending onthe mean molar weight of the PSS, optimum amounts used can be determinedaccording to diverse criteria. For mean molar weights of 5000 to 1 000000 g/mol, the preferred amounts used are in the range from 10 to 800mg/litre of anion exchanger.

Separability of the mixed beds, however, is only achieved onsimultaneous treatment of the cation exchange component as described,for example, in EP-A 1 291 083. In this case also, use is made ofwater-soluble polyelectrolytes, for example polyvinylaromatic quaternaryammonium salts, polyvinylaromatic amino acid salts andpolyvinylpyridinium salts having mean molar weights of 5000 to 1 000 000g/mol.

The above processes all have the disadvantage that the polyvinylaromaticacids or ammonium compounds are only accessible in the suitable molarmass range with relative difficulty and that to achieve goodseparability in the mixed bed both charge components must be treated.

An object of the present invention was to overcome the describeddisadvantages.

DISCLOSURE OF THE INVENTION

A solution of the object and thus subject matter of the presentinvention is a process for producing non-agglomerating readily separablemixed bed ion exchangers or mixed bed components, characterized in thatthe anion exchange component, before or after mixing with the cationexchange component, is treated with a condensate of one or more aromaticsulphonic acids in the application concentrations of 10 mg/litre ofresin to 100 g/litre of resin.

Surprisingly, the sole treatment of the anion exchange componentaccording to the invention produces a non-agglomerating readilyseparable mixed bed having excellent desalting performance.

The process according to the invention provides solely treatment of theanion exchange component with oligomeric aromatic sulphonic acidcondensates as are used, for example, as tanning agents and liquefiers.These sulphonic acid condensates are already disclosed by EP-A 0 037 250or DE-A 2 934 980. Aromatic sulphonic acids in the context of thisinvention are also taken to mean sulphomethylated aromatics. Preferredsulphonated aromatics are: phenolsulphonic acid, sulphonated ditolylether, 4,4′-dihydroxydiphenylsulphone, sulphonated diphenylmethane,sulphonated biphenyl, sulphonated terphenyl, naphthalenesulphonic acidsor benzenesulphonic acids. Further formulations for the composition ofthe claimed product group are described in EP-A 816 406, the contents ofwhich are hereby incorporated by the present application. Condensationof the sulphonic acids proceeds in this case with aldehydes or ketones.Here, in particular aliphatic, cycloaliphatic and also aromaticrepresentatives come into consideration. Preference is given toaliphatic aldehydes, with use being made particularly preferably offormaldehyde and also other aliphatic aldehydes having 3-5 carbon atoms.

These condensates are generally in the form of their alkali metal,alkaline earth metal or ammonium salts and are accompanied by “neutralsalts” from synthesis-specific neutralization reactions. The use ofthese condensates can, but need not, proceed in the form of theirlow-salt formulations, the production of which is described, forexample, in EP-A 0 816 406. Quite in contrast, salt additions canobviously improve the take-up behaviour of the condensates, which isdemonstrated in measurably improved desalting performance (Example 5,FIG. 3). In a preferred embodiment, therefore salt is added to the anionexchange component, particularly preferably alkaline earth metal salts.Use is made particularly preferably of calcium chloride.

In the broader sense, the condensed aromatic sulphonic acids are alsotaken to mean ligninsulphonates and condensates thereof with aromatichydroxyl compounds.

Ion exchange resins as are described in this invention are typicallyspherical polymer beads having a diameter of 0.15-1.20 mm, preferablyhaving a diameter of 0.25-1.00 mm.

Of particular interest here are strongly acidic cation exchangers andstrongly basic anion exchangers based on monovinylaromatics, preferablystyrene, or alkyl-substituted offshoots which are copolymerized withcrosslinkable monomers. As crosslinkers in this sense, use is preferablymade of divinylbenzene (or alkyl-substituted related compounds),octadiene, trivinylcyclohexane and ethylene glycol-bridged divinyl etheror divinyl acrylates and divinyl methacrylates.

Particular preference is given to strongly acidic cation exchangerswhich are obtained by sulphonation from the abovementioned polymers andstrongly basic anion exchangers having quaternary ammonium groups whichwere synthesized from the abovementioned polymers by aminomethylation(chloromethylation processes or phthalimide processes). It is of nosignificance here whether the abovementioned ion exchange resins are inthe form of what are termed gel-like or macroporous (polymerization ofthe abovementioned starting materials in the presence of an inertsolvent/precipitant) species. In addition, the activity is independentof the salt form of the anion exchange component to be treated (forexample chloride, sulphate, hydroxide). Ion exchangers which arepreferably to be treated by the process according to the invention arethe following:

-   -   strongly acidic gel-type cation exchangers, for example LEWATIT®        MonoPlus S 200    -   strongly acidic macroporous cation exchangers, for example        LEWATIT® MonoPlus SP 112    -   strongly basic gel-type anion exchangers, for example LEWATIT®        MonoPlus M 500    -   strongly basic macroporous anion exchangers, for example        LEWATIT® MonoPlus MP 500

Particularly preferred representatives of said sulphonic acidcondensates for the process according to the invention are thefollowing:

RETINGAN® ZN, TAMOL® NN4501, TAMOL® NH7519—methylene-condensednaphthalene-sulphonic acid(s) [NSSK=naphthalenesulphonic acidcondensates or NSS=methylene-condensed naphthalenesulphonic acid]

BAYKANOL® SL—methylene-condensed sulphonated ditolyl ether

TANIGAN® BN—methylene-condensed naphthalenesulphonic acid(s) and4,4′-dihydroxydiphenyl-sulphone.

Preferably, according to the invention, the polyanionic component isapplied to the anion exchanger in the batch.

Preferably according to the invention, in the production of mixed beds,the anion exchanger is treated before regeneration of the anionexchanger and before mixture with the cation exchange component.Alternatively, however, retrospective treatment is likewise possible.

According to the invention, very particularly preferably, as sulphonicacid condensates, use is made of methylene-bridged naphthalenesulphonicacids [NSSK]. Particularly preferably, the sulphonic acid condensateshave a molar weight of >1000 g/l, preferably >5000 g/l and veryparticularly preferably >20 000 g/mol.

EXAMPLES Example 1

The anion exchange resin to be treated (LEWATIT® MonoPlus M 500) wascharged in a glass beaker with the specified amount of condensate as a0.1% strength solution. The mixture was stirred for 20 min and thenallowed to stand for a further 10 min. Thereafter it was dewatered andwashed with 2 BV (bed volumes) of deionized water.

50 ml of the anion exchange resin thus treated were shaken under wateron a vibrating bench to constant volume and mixed with the same volume(shaken under water) of a strongly acidic cation exchanger (LEWATIT®MonoPlus S 200) by stirring in a glass beaker. Subsequently the mixturewas shaken under water on the vibrating bench. The volume of the mixturewas determined. Results with different condensates in differentapplication rates may be found in Table 1.

Example 2

The anion exchange resin to be treated (LEWATIT® MonoPlus M 500) wasadmixed in a glass beaker with 1.5 g/(litre of resin) of the NSScondensate 2, dissolved in demineralized water, with stirring. Themixture was then allowed to stand for 10 min. Thereafter it wasdewatered and washed with 2 BV of deionized water. Regeneration proceedsvia treatment with 300 g of NaOH 100%/l of resin as 5% strength solutionwhich was passed through the bed.

250 ml of the anion exchange resin thus treated were shaken under wateron a vibrating bench to constant volume and mixed with 160 ml (shakenunder water) of a strongly acidic cation exchanger (LEWATIT® MonoPlus S200) by stirring in a glass beaker. Subsequently the mixture wastransferred to an exchange column and charged with 10 BV of drinkingwater.

By water flowing in at the column bottom, the bed was then extended forthe regeneration to about three times its height. After approximately 2min the flow of the influent water was continuously reduced to the valueof zero. Thereafter, the column was carefully dewatered until just abovethe ion exchange bed. The anion exchanger was be seen at the top and thecation exchanger at the bottom. The volumetric fractions of the two weredetermined. An anion exchange fraction of 61% gave very good separation.

NSSK additions (1 g/l of anion exchange component) were introduced intothe liquid standing over the mixed bed. The liquid level was thenlowered again to the bed level. After 10 min, extension of the bed bywater flowing in from the bottom began.

Example 3

The anion exchange resin to be treated (LEWATIT® MonoPlus MP 500) wascharged in a glass beaker with 1.5 g/(litre of resin) ofnaphthalenesulphonic acid condensate 1 as 0.1% strength solution or with1.25 g/(litre of resin) of sulphonated polystyrene (Versa® TL 130). Themixture was stirred for 20 min and then allowed to stand for a further10 min. Thereafter it was dewatered and washed with 10 BV of deionizedwater.

Example 4

Test Structure:

Test volume approximately 400 ml Flow rate: 270 g 28.5 BV 11.4 l/h

Pretreatment of the Samples from Example 3:

Regeneration with 300 g/l of HCl/NaOH 100%, when non-regenerated resinmixtures were tested. [KR/OH regeneration: NaOH—H₂SO₄—NaHCO₃—NaOH→degreeof regeneration>90%]

In the case of complete mixtures, the resins must be thoroughly mixedbefore the start of the experiment.

Before the start of the test, the sample was washed exhaustively with 10BV.

Measurement Instruments:

Anatel ® 1000 for total capacity Thornton ® 770 PC for resistance

Test Steps:

1. Washing until maximum resistance value was achieved in the effluent(approx. 1 h)

2. Charging with raw water until breakthrough (<1 MΩ)

Washwater Quality:

Resistance: >18.2 MΩ TOC: 1-3 ppb

Charging Water Quality:

Conductivity: 450-500 μS/cm Salt content: 5-6 meq/l SiO₂ content: 3-4ppm

The reduction in agglomeration is measurable using a conventional methodas described in Example 1. A satisfactory degree of “non-agglomeration”is achieved when the combined (shaken) volumes of anion and cationexchangers after mixing is no more than 20%, preferably no more than10%, and particularly preferably no more than 5%, above the total volumeof the separated resins.

Results according to Example 1 are compiled in Table 1.

Example 5

600 ml samples of anion exchanger were each mixed with 600 ml ofsolution (a: demineralized water, b: 1% strength CaCl₂ solution indemineralized water) in a glass column and vortexed by air flowing infrom the bottom. In the course of 45 min, 0.72 g of a 5% strengthsolution of the naphthalenesulphonic acid condensate 2 in demineralizedwater was added with vortexing (equivalent to 60 mg of NSSK2 per litreof anion exchanger). After addition was completed, vortexing wascontinued for a further 15 min. Thereafter the solution was allowed todrain out and the column was made up with demineralized water to 1 cmabove the resin surface before charge exchange using 2400 g of sulphuricacid (3% strength). A neutral wash follows. Thereafter the charge wasexchanged to the OH form using 2395 g of a 10% strength sodium hydroxidesolution. Finally it was washed neutral and mixed for measurement withLEWATIT® MonoPlus S 200 KR (FIG. 3).

Table 1: Mixed bed agglomeration test according to Example 1. Mixture ofLEWATIT® MonoPlus M500 and LEWATIT® MonoPlus S 200. The amount ofcondensates used is reported. The inorganic salt contained in thecommercial products has not been taken into account.

Additive name and application rate Volume shaken “Blank test” 167 mlNaphthalenesulphonic acid condensate 1 0.50 g/litre of resin 102 ml 0.10g/litre of resin 101 ml 0.05 g/litre of resin 145 mlNaphthalenesulphonic acid condensate 2 0.10 g/litre of resin 102 ml 0.05g/litre of resin 102 ml Sulphonated ditolyl ether sulphonated, condensed0.50 g/litre of resin 101 ml 0.10 g/litre of resin 103 ml 0.05 g/litreof resin 152 ml Naphthalenesulphonic acid and4,4′-dihydroxydiphenylsulphone co-condensed 0.50 g/litre of resin 101 ml0.10 g/litre of resin 140 ml

For regeneration, the mixed beds must first be fractionated into theindividual components. This generally proceeds by the means that wateris injected into the exchange columns from the bottom. In the waterstream, the components are ordered in accordance with their density: theanion exchanger is situated above the cation exchanger. The separationlayer may be readily identified on the basis of the colour differencesof the components. A precondition for as complete a regeneration aspossible of the mixed bed (that is to say of its individual components)is good separation into anion exchange and cation exchange components.This separation, however, is virtually not achieved in the case ofuntreated starting materials and only inadequately in the case of anionexchange component treated in advance. If, then, before separation asmall amount of the compounds of the invention is added, with mixing asis customary by injection of air or nitrogen, subsequently the mixed bedmay be fractionated virtually perfectly into the individual componentsin the water upflow (Example 2).

In order to test the separability of the mixed bed, a method wasemployed in which the production of a mixed bed ion exchanger, its usefor obtaining ultrapure water and subsequent separation of the mixed bedinto its components in the upflow process is simulated (Example 2). Inthis process 61 parts of a strongly basic anion exchanger are mixed with39 parts of a strongly acidic cation exchanger, transferred to a columnand subsequently operated in the desalting mode for producing highpurity water. After a certain running time, the components are separatedfrom one another in the water upflow. The material is allowed to settle,dewatered and the visually recognizable percentage composition of themixture is determined. Perfect separation is given by an anion exchangefraction of 61%. The results may be found in Table 2.

TABLE 2 Results of the mixed bed separation test according to Example 2Volume of the anion Ser. Cation Anion Additive before exchanger afterNo. exchanger exchanger separation separation 1 untreated untreated NoNo separation 2 untreated untreated NSS Condensate 2 61% 3 untreated NSSNo 25% Condensate 2 4 untreated NSS NSS Condensate 2 60% Condensate 2

Effect of Treatment on Mixed-Bed Performance

The loading of the anion exchanger in this case is without any adverseeffect on the performance of the mixed bed produced correspondingly.Rather, in partial aspects, the performance is even improved (FIG. 1),and this also in comparison with a sample produced analogously to U.S.Pat. No. 5,902,833 (Example 3).

In addition to the important property of separability, preventingagglomeration has a considerable effect on performance of the resinmixture with respect to extractability and exchange kinetics. Clumping,even in the micro region, leads to channel formation in flow through thebed, that is to say individual regions of the resin bed, through whichflow generally passes from top to bottom, are not wetted and thus do notparticipate in the exchange.

More serious than the channel formation is the material transfer whichis produced by mechanical breakage, such as due to air vortexing orstirring of the clumping. Since the anion exchange component has thesofter surface, generally anion exchange material is transferred to thecation exchanger. The longer and more serious is the action of themechanical stress, the more material is transferred. Since thefunctional group of the anion exchanger is a cation, the surface of thecation resin becomes loaded with cations owing to the material transfer.This leads to a poorer mass transfer as a result of this covering layerwhich in turn has an adverse consequence on slip. The more strongly thecovering layer is formed, the higher is the cation slip and the lower isthe resistance of the solution in the effluent downstream of the resinmixture. This can only be counteracted by markedly reducing or evencompletely suppressing the clumping by a suitable coating.

Notes on FIGS. 1 to 3:

The performance of a resin mixture is defined by the followingmeasurable characteristics:

Resistance of the prepared water on washing

Resistance of the prepared water on loading

SiO₂ slip on loading

Usable capacity

The ‘usable capacity’, expressed in eq/l, is a measure of the ionexchange capacity effectively available up to breakthrough for a definedendpoint, such as, for example, a minimum residual resistance of 17 MΩ.For this, the ion loading of the loading water in eq/l is multiplied byflow rate in 1/h and the time up to breakthrough point in h. This givesthe ion loading which is divided by the amount of resin in litres.

FIG. 1 Presentation of the experimental results of differently treatedresin samples including the blank sample (Example 3) and measurementaccording to Example 4; NSSK=naphthalene-sulphonic acid condensate,PSS=polystyrenesulphonic acid).

For identical parameters with respect to flow rate and ion loading ofthe raw water, as in the experiments in FIG. 1, the time to breakthroughcan be used as a sufficient comparison index (experimental procedureExample 4).

FIG. 1 shows the results of a test series using LEWATIT® MonoPlus MP500,which was regenerated after treatment with NSSK or PSS with 300 g ofNaOH 100%/l . Thereafter, it was mixed with an untreated cationcomponent of the LEWATIT® MonoPlus SP112 H type in the ratio cations toanions 1:1.5. The cation exchanger, for better comparability, wasprovided in the regenerated form. For better comparability, resinsamples of the same production batch were used.

FIG. 1 shows the capacity which is higher by orders of magnitude of themixed beds produced with polyanion-occupied anion exchange componentscompared with the blank sample (magenta). The NSSK-treated sample has ahigher capacity than that treated with PSS.

The untreated sample cannot be washed to values greater than 17 MΩ(starting point of the graph at 0 min). The sample treated with NSSK 1may be washed to the theoretical resistance of pure water of 18.3 MΩ.The PSS-treated samples likewise achieved an acceptable level.

On loading, again the NSSK 1-treated sample achieved the bestperformance, with respect to the longest time to the breakthrough pointof 17 MΩ.

The untreated sample was too poor kinetically to reduce the salt contentto a sufficient extent.

A similar picture results in the study of gel-type mixed bed exchangers(FIG. 2). The untreated sample is too poor in the mixed bed to be ableto decrease the salt content sufficiently. The treated samples reach therequired resistance values. The differing usable capacities result fromregeneration processes of differing effectiveness (Example 4).

FIG. 2 Presentation of the experimental results of differently treatedresin samples of the same batch LEWATIT® MonoPlus M 500 in a mixed bedwith LEWATIT® MonoPlus S 200 KR. Loading amounts with NSSK 1 and type ofregeneration may be found in the legend [Measurements according toExample 4; NSSK=naphthalenesulphonic acid condensate].

On minimizing the amounts used of the compounds of the inventionselected for the coating, by addition of salt, the take-up behaviour canbe improved and thus a good desalting performance in the mixed bed canbe achieved even with very low rates of addition.

The action of calcium chloride addition on charging LEWATIT® MonoPlus M800 with naphthalenesulphonic acid condensate 2 is shown impressively inFIG. 3: despite equally low usage of NSSK 2, the desalting performanceof the sample produced in the presence of calcium chloride is markedlybetter than the “blank sample”. No adverse effect on the alkaline earthmetal salt used was observable at any time point.

Summary: Polyanion additions to anion exchange components in mixed bedsare able to reduce the clumping effectively or prevent it completelywith the effect that correspondingly treated mixtures more rapidlyachieve the required resistance level in the eluate (or only suchmixtures achieve this level at all) and have a higher usable capacitythan corresponding mixtures without additive addition. In experiments,NSSK-treated mixtures demonstrated better measured values thanPSS-treated comparisons.

The sole addition of the claimed compounds to the anion exchangecomponent in mixed beds makes possible the effective separation in theupflow process for regeneration of the component.

FIG. 3 is a presentation of the experimental results of resin sampleswhich are identically treated with naphthalenesulphonic acid condensate2 of the same batch of LEWATIT® MonoPlus M 800 with and without thepresence of calcium chloride (Example 5) in the mixed bed with LEWATIT®MonoPlus S 200 KR. The measurement, in a departure from the descriptionin Example 4, was not performed with “raw water”, but with sodiumchloride solution (500 ppm).

1. A process for producing non-agglomerating readily separable mixed bedion exchangers or mixed bed components, wherein the anion exchangecomponent, before or after mixing with the cation exchange component, istreated with a condensate of one or more aromatic sulphonic acids in theapplication concentrations of 10 mg/litre of resin to 100 g/litre ofresin.
 2. A process according to claim 1, wherein the sulphonic acidsfor producing the condensates are phenolsulphonic acid, sulphonatedditolyl ether, 4,4′-dihydroxydiphenyl-sulphone, sulfonateddiphenylmethane, sulfonated biphenyl, sulfonated terphenyl,naphthalenesulphonic acids or benzenesulphonic acids.
 3. A processaccording to claim 2, wherein methylene-bridged naphthalenesulphonicacids [NSSK] are used as naphthalenesulphonic acid.
 4. A processaccording to claim 1, wherein the sulphonic acids are condensed withaldehydes or ketones.
 5. A process according to claim 1, wherein thepolyanionic component is applied to the anion exchanger in the batch. 6.A process according to claim 1, wherein for producing mixed beds, theanion exchanger is treated before regeneration of the anion exchangerand before mixing with the cation exchange component.
 7. A processaccording to claim 1, wherein the sulphonic acid condensates have amolar weight of >1000 g/l.
 8. A process according to claim 1, whereinsalt is added in treatment of the anion exchange component.
 9. A processaccording to claim 8, wherein the salt added is an alkaline earth metalsalt.
 10. A method of using of condensates of one or more aromaticsulphonic acids in the application concentrations of 10 mg/litre ofresin to 100 g/litre of resin for producing non-agglomerating, readilyseparable mixed bed ion exchangers or mixed bed components by treatingthe anion exchange component before or after it was mixed with thecation exchange component.